- Philatelic & Numismatic Society
- Robotics Club
- Yoga Club
- Library Club
- Environmental Club
- College Magazine
- Chamber Orchestra
- Cinema Society
- Astronomy Club
- Aquarium Club
- Scuba Diving Unit
- Culinary Arts Society
- Aeronautical Societya
- Junior Science & Technology
- Histoarcheo Club
- Geography Society
- Gavel Club
- Student Christian Movement
- English Lit & Debating Society
- Radio Club
- Junior Maths Society
- Road Safety Patrol
- Sinhala Literary & Debating Society
- Seylan Bank Students’ Savings Unit
- HNB Students’ Savings Unit
- Kennel Club
- Buddhist Students’ Association
- Junior English Lit & Debating Society
- Art Club
- Spelling Union
- Carnatic Orchestra
- Canto Perpetua Choir
- Western Band
- Tamil Drama Society
- Hewisi Band
- English Drama Society
- Photographic Club
- Society for Social Work & Welfare
- ICT Society
- Senior Environmental Club
- Hindu Students’ Union
- Political Science Society
- Red Cross Society
- Association of Innovation and Design
- Islamic Society
- Association of Science and Technology
- Quiz Club
- Automobile Club
- Cubing Society
- Health Club
- Tamil Literary and Debating Society
- Wildlife Society
- Thomian Union
- Commerce Society
- Interact Club
- The Ternion
- Classical Music Association
- Media Unit
- Productive Citizenship Society
- United Nations Club
Western Band
The Western Band of S. Thomas’ College, Mount Lavinia, was established in 1970, during the tenure of Warden Anandanayagam, and made its debut at the Old Boy’s Tea Party, on the 13th of February. Ever since, the Western Band has been involved by accompanying the community of S. Thomas’ College, by performing at many occasions, such as the Annual Prize Giving, weekly assemblies, and the Inter-House Sports Meet, to name a few.Latest Project
Musica Perpetua: The Thomian Bandsmen Back in Concert
Dating back to 2017, the "Music Perpetua" series of concerts have filled the air with music, and showcased the talents of the Thomas bandsmen. The most recent concert was held at the Lionel Wednt theatre, in February 2020, under the leadership of R. Abirthan, and the band entertained the audience, by performing many hits from famous songwriters, such as Twist and Shout, Staying Alive, and New York to name a few.

